using System;

namespace monisha

{

public class Program

{

    public static void Main()

    {

        int a,b,c,p;

        double area;

        Console.WriteLine("enter the sides");

        a = int.Parse(Console.ReadLine());

        b = int.Parse(Console.ReadLine());

        c = int.Parse(Console.ReadLine());

        p = a+b+c;

        p = p/2;

        area = Math.Sqrt(p*(p-a)*(p-b)*(p-c));

        Console.WriteLine(area);

    }

}

}